Piezoelectric ceramic compositions

ABSTRACT

Ceramic compositions within the polygonal area defined by the formulas Pb(Mn1/3Ta2/3)0.030Ti0.470Zr0.500O3 Pb(Mn1/3Ta2/3)0.250Ti0.500Zr0.250O3 Pb(Mn1/3Ta2/3)0.375Ti0.375Zr0.250O3 Pb(Mn1/3Ta2/3)0.250Ti0.125Zr0.62503 ARE PARTICULARLY USEFUL FOR MAKING TRANSDUCER ELEMENTS. The composition Pb(Mn1/3Ta2/3)0.250Ti0.430Zr0.320O3 shows a high resonant frequency stability with temperatures within the range from -20* to 80* C.

[ 51 Mar. 28, 1972 [54] PIEZOELECTRIC CERAMIC COMPOSITIONS [72] Inventors: l-liromu Ouchi; Masamitsu Nishida, both of Osaka, Japan Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka, Japan 22 Filed: Sept. 4, 1968 211 Appl.No.: 757,338

[73] Assignee:

[30] Foreign Application Priority Data Oct. 27, 1967 Japan ..42/6977O 52 us. Cl. ....2s2/62.9, 106/39 R [51] llnt. CI. ...C04b 35/46, C04b 35/48 [58] Field of Search ..252/62.9; 106/39 [56] References Cited UNITED STATES PATENTS 3,268,453 8/1966 Ouchi et a1. ..252/62.9 3,268,783 8/1966 Saburi ..l06/39 3,400,076 9/1968 Ouchi et al. ..252/62.9

' The Composition M Primary ExaminerTobias E. Levow Assistant ExaminerJ. Cooper AttorneyWenderoth, Lind & Ponack 57 ABSTRACT Ceramic compositions within the polygonal area defined by the formulas are particularly useful for making transducer elements.

shows a high resonant frequency stability with temperatures within the range from -20 C to 80 C.

2 Claims, 2 Drawing Figures PATENTEnmRze I972 3652413 Fig. l

IIiromu Ouchi and Masamitsu Nishida,

Inventors LNWlMld-ZJJI 1 M,

Attorneys PIIEZOELECTRIC CERAMIC COMPOSITIONS This invention relates to piezoelectric ceramic compositions and articles of manufacture fabricated therefrom. More particularly, the invention pertains to novel ferroelectric ceramics which are polycrystalline aggregates of certain constituents. These piezoelectric compositions are sintered to ceramics by per se conventional ceramic techniques and thereafter the sintered ceramics are polarized by applying a DC (direct current) voltage between the electrodes to impart thereto electromechanical transducing properties similar to the well-known piezoelectric effect. The invention also encompasses the calcined product of raw ingredients and the articles of manufacture such as electromechanical transducers fabricated from the sintered ceramic.

The ceramic bodies materialized by the present invention exist basically in solid solution comprising the ternary system Pb(Mn Ta )O PbTiO PbZrO The use of piezoelectric materials in various transducer applications in the production, measurement and sensing of sound, shock, vibration, pressure, etc. has increased greatly in recent years. Both crystal and ceramic types of transducers have been widely used. But, because of their potentially lower cost and facility in the fabrication of ceramics with various shapes and sizes and their greater durability for high temperature and/or for humidity than that of crystalline substances such as Rochelle salt, piezoelectric ceramic materials have recently achieved importance in various transducer applications.

The piezoelectric characteristics required of ceramics vary with different applications. For example, electromechanical transducers such as phonograph pickups and microphones require piezoelectric ceramics characterized by a substantially high electromechanical coupling coefiicient and dielectric constant. On the other hand, in filter applications of piezoelectric ceramics, it is desired that the material exhibits a higher value of mechanical quality factor and high electromechanical coupling coefficient. Furthermore, ceramic materials require a high stability with temperature and time in resonant frequency and in other electrical properties.

As more promising ceramic for these requirements, lead titanate-lead zirconate is in wide use up to now. However, it is difficult to get a very high mechanical qualityfactor along with high planar coupling coefficient in the lead titanate-lead zirconate ceramics. And the dielectric and piezoelectric properties of the lead titanate-lead zirconate ceramics change greatly with firing technique, which is ascribable to evaporation of PhD.

It is, therefore, the fundamental object of the present invention to provide novel and improved piezoelectric ceramic materials which overcome at least one of the problems outlined above. A more specific object of the invention is to provide improved polycrystalline ceramics characterized by very high mechanical quality factor along with high piezoelectric coupling coefficient.

Another object of the invention is the provision of novel piezoelectric ceramic compositions, certain properties of which can be adjusted to suit various applications.

A further object of the invention is the provision of improved electromechanical transducers utilizing, as the active elements, an electrostatically polarized body of the novel ceramic compositions.

These objects of the invention and the manner of their attainment will be readily apparent from a reading of the following description and from the accompanying drawing, in which:

FIG. I is a cross-sectional view of an electromechanical transducer embodying the present invention.

FIG. 2 is a triangular compositional diagram of materials utilized in the present invention.

Before proceeding with a detailed description of the piezoelectric materials contemplated by the invention, their application in electromechanical transducers will be described with reference to FIG. 1 of the drawings wherein reference character 7 designates, as a whole, an electromechaiiical transducer having, as its active element, a preferably discshaped body 1 of piezoelectric ceramic material according to the present invention.

Body 1 is electrostatically polarized, in a manner hereinafter set forth, and is provided with a pair of electrodes 2 and 3, applied in a suitable and per se conventional manner, on two opposed surfaces thereof. Wire leads 5 and 6 are attached conductively to the electrodes 2 and 3 respectively by means of solder 4. When the ceramic is subjected to shock, vibration or other mechanical stress, the generated electrical output can be taken from wire leads 5 and 6. Conversely, as with other piezoelectric transducers, application of electrical voltage to electrodes 2 and 3 will result in mechanical deformation of the ceramic body. It is to be understood that the term electro-mechanical transducer as used herein is taken in its broadest sense and includes piezoelectric filters, frequency control devices, and the like, and that the invention may also be used and adapted to various other applications requiring materials having dielectric, piezoelectric and/or electrostrictive properties.

According to the present invention, the ceramic body 1, FIG. 1, is formed of novel piezoelectric compositions which are polycrystalline ceramics composed of Ib(Mn,,:,Ta,,,, )O PbTiO PbZrO.

The present invention is based on the discovery that within particular ranges of this ternary system, the specimens exhibit a very high mechanical quality factor along with high planar coupling coefficient.

The present invention has various advantages in manufacturing process and in application for ceramic transducers. It has been known that the evaporation of PhD during firing is a problem in sintering of lead compounds such as lead titanate zirconate. The inverted composition, however, shows a smaller amount of evaporated PbO than usual lead titanate zirconate does. The ternary system can be fired without any particular control of PbO atmosphere. A well sintered body of the present composition is obtained by firing in a ceramic crucible with a ceramic cover made of A1 0 ceramics. A high sintered density is desirable for humidity resistance and high piezoelectric response when the sintered body is applied to a resonator and others.

All possible compositions coming within the ternary system Pb(Mn Ta )O PbTiO;,PbZrO are represented by the triangular diagram constituting FIG. 2 of the drawings. Some compositions represented by the diagram, however, do not exhibit high piezoelectricity, and many are electromechanically active only to a slight degree. The present invention is concerned only with those compositions exhibiting piezoelectric response of appreciable magnitude. As a matter of convenience, the planar coupling coefficient (K,,) of test discs will be taken as a measure of piezoelectric activity. Thus, within the area bounded by lines connecting points ABCD, FIG. 2, all compositions polarized and tested showed a planar coupling coefficient of approximately 0.22 or higher. The compositions in the area of the diagram bounded by lines connecting points A, B, and E, FIG. 2, exhibit a planar coupling coefficient of approximately 0.35 or higher, the molar percent of the three components of the compositions ABCDE being as follows:

P (Mn,,;Ta,,- )O; PbTiO, IbZrO A 3.0 47.0 50.0 B 25.0 50.0 25.0 C 37.5 37.5 25.0

Furthermore, the compositions near the morphotoropic phase boundary of the ternary system, particularly 1/3 2/3)0.25 0.as 'u.a1 a and 1/3 21a)o.i3 0.42 'o.4s a, give ceramic products having a planar coupling coefficient of 0.5 or higher.

According to the present invention, the piezoelectric and dielectric properties of the ceramics can be adjusted to suit various applications by selecting the proper composition.

The compositions described herein can be prepared in acing firing.

The sintered ceramics are polished on both surfaces to the thickness of l millimeter. The polished disc surfaces may then be coated with silver paint and fired to form silver electrodes.

cordance with various per se Well-known ceramic procedures- 5 Finally, the discs are polarized while immersed in a bath of sil- A referred method, r, hereinafter more full icone oil at 100 C. A volta e radient of DC 4 kv. er mm. is

Y 2 g P described, consists in the use of PbO or Pb O MnO or maintained for 1 hour, and the discs are field-cooled to room 3 4 2 5 Tioz, ztemperature in 30 minutes.

Stamng mammals Oxide P' nlangaflese The piezoelectric and dielectric properties of the polarized d.loxld.e (Mno2) tantalum Pemoxlde gazes) mama (Fl-'02) specimen have been measured at 20 C. in a relative humidity zlrconra (ZrO,), all of relatively pure grade (e.g., grflde) of 50 percent and at a frequency of l kc. Examples of specific are mnmately mlxed m rubber'lmed ban mm mm dlsuued ceramic compositions according to this invention and various In mlnmg f l shoulfl be exerclsed to pertinent electromechanical and dielectric properties thereof avoid, f p p ofmgl'edlffllts Vaned to compensate are given in the Table, infra. Conventional compositions do comafnmmlon by W of the 2 9 not comprise any in which both the mechanical quality factor Following the wet m1ll1ng, the mixture is dried and mixed to (QM) and the planar coupling coefficient Show high values. assure as homogeneous a mixture as possible. Thereafter, the From the Table it will be readily evident that the exem la mixture is suitably formed into a desired form at a pressure of p ry 400 compositions selected from the area bonded by lines connect- 1 ograms per square centimeter. The compacts are preo ing polnts ABCD of the diagram of FIG. 2 are characterized reacted by calclnatron at a temperature of around 850 C. for by very high mechanical q y factor and g planar 2 182 l th t d t l n d t 1 coupling coefficient. With the aid of the said Table, the values d 5 9 d t e s T 3 owe coo of mechanical quality factor, planar coupling coefficient and an is en we e o a par e Slzej nee ,agamicare dielectric constant can be adjusted to suit various applications should be exercised to avoid, or the proportions of ingredients by Selecting the appropriate Composition l G 8 compensate cmgammanon by wear of the In addition to the superior properties shown above, commlnmg or stones ,Depen mg on preference h positions according to the present invention yield ceramics of fP desu'ed f malenal m be i a mm or sup good physical quality and which polarize well. Thus, the ternasuitable for press1ng,sl1p castmg, or extruding, the case may ry ceramic Pb (Mm/Jae3)O3Pb-1-iO3 PbZrO3 forms an CXCCL be, in accordance with per se conventlonal ceramic 1cm piezoelectric ceramic body Procedures The composition, Pb(Mn),, Ta Ti Zr O shows The samples whlch data are hereulbelow f a high resonant frequency stability with temperatures within p p f y mlxmg grams of the mllled Preslmered the range from 20 to 80 C. The change in resonant frequenture with 5 cc. of distilled water. The mix was then pressed Cy i 1 m These properties are important to the use of into discs of 20 mm. diameter and 2 mm. thickness at a pres- 35 i d n-i compositions in fil applications TABLE Mole percent of composition 24 hours after palin Diclectric Planar Mechanical Example constant, e coupling quality Number Pb(MI1 /3T8z/3)O3 PbtiO; PbZrOz at l kc./s. coeif K factor, QM

What is claimed is: l. A piezoelectric ceramic material consisting of the solid solution having the following formula: ua zla)0.250 o.4ao '0.a2o 3 2. An electromechanical transducer element comprising an electrostatically polarized solid solution ceramic consisting of a ceramic composition as claimed in claim 1. 

2. An electromechanical transducer element comprising an electrostatically polarized solid solution ceramic consisting of a ceramic composition as claimed in claim
 1. 